APS symptoms can vary because antiphospholipid syndrome (APS) primarily increases the risk of abnormal blood clots rather than causing one specific set of symptoms. A clot in a leg may cause swelling, pain, warmth, or redness, while a lung clot can cause sudden shortness of breath, chest pain, or coughing. Clots affecting the brain may produce sudden weakness, numbness, speech difficulties, or other neurological changes. APS can also be associated with pregnancy complications, including recurrent pregnancy loss. Some people have antiphospholipid antibodies without developing symptoms or clots. Diagnosis requires appropriate medical evaluation and blood testing rather than symptoms alone. Sudden breathing difficulty, chest pain, or neurological symptoms require emergency medical attention.